The present invention relates to a heat developable photosensitive material, and specifically to a heat developable photosensitive material suitable for photomechanical process.
Recently, in photomechanical process field, a decrease in processing effluent has been strongly demanded from the viewpoint of environmental protection as well as of storage space saving. Accordingly, techniques regarding heat developable photosensitive materials for use in the photomechanical process are demanded which are capable of being subjected to efficient exposure utilizing laser scanners or laser image setters and of forming clear black images with high resolution as well as high sharpness. These heat developable photosensitive materials make it possible to eliminate the use of liquid based processing chemicals and to supply the market with a simple heat developable processing system which protects the environment.
Methods which form images utilizing heat development are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075, and D. Morgan and B. Shely, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d in Imaging Processes and Materials, Neblette, 8th Edition, edited by A. Sturge, V. Walworth, and A. Shepp, page 2, 1969. Such heat developable photosensitive materials (hereinafter referred to simply as photosensitive materials) generally comprise reducible non-photosensitive silver sources (for instance, organic silver salts), photocatalysts (for example, silver halides) in workable amounts as photocatalysts, and silver reducing agents which are commonly dispersed into an organic binder matrix. Said photosensitive materials are stable at normal temperature. However, when they are heated to a relatively high temperature (for example, 80xc2x0 C. or higher) after exposure, silver is formed through a redox reaction between said reducible silver sources (which function as the oxidizing agents) and said reducing agents. Said redox reaction is promoted by catalytic action of a latent image formed by exposure. Silver, which is formed by the reaction of reducible silver salts in the exposed area, provides a black image in contrast to the unexposed area, whereby a visible image is formed.
Heretofore, this type of heat developable photosensitive material has been known, and the photosensitive layer of most of these photosensitive materials is formed by applying a coating composition in which organic solvents such as toluene, methyl ethyl ketone (MEK), methanol, and the like, are employed. The use of organic solvents as the solvents results in such disadvantages as adverse effects to human body in the production process, and an increase in cost for solvent recovery and the like.
Accordingly, methods have been developed in which the photosensitive layer is formed employing a coating composition comprised of water as the solvent, which largely overcomes said drawbacks. For example, Japanese Patent Publication Open to Public Inspection Nos. 49-52626, 53-116144, and others describe examples in which gelatin is employed as the binder. Employing gelatin as the binder exhibits great advantages in productivity as well as in environmental protection. However, photographic properties are markedly degraded and problems occur in which black silver images become brown; when a photosensitive layer is touched with fingers before exposure, fingerprints result in desensitization; and the like.
Further, it is known that without employing gelatin, coating is carried out employing a water based coating composition comprised of polymer latex as the binder (for example, in Japanese Patent Publication Open to Public Inspection Nos. 11-316437, 11-316438, and others). However, in such cases, problems occur in which uneven density due to development tends to be noted, and linearity deteriorates.
An objective of the present invention is to provide a heat developable photosensitive material which results in improvements in image color, uneven density, and linearity.
The invention and the embodiments are described hereunder.
A heat developable photosensitive material comprising a support, a first layer containing an organic silver salt, photosensitive silver halide and a reducing agent, and a second layer which is provided on same side of the first layer and farther from the support than the first layer, wherein
the first layer is formed by coating a first coating composition containing the organic silver salt, the photosensitive silver halide, the reducing agent, polymer latex in an amount of at least 30 percent by weight of the first layer in dried state and a solvent, the solvent comprising water in an amount of at least 50 percent by weight of the solvent, and
the second layer is formed by coating a second coating composition comprising a polymer latex in an amount of at least 50 percent of the second layer in dried state and a solvent, the solvent comprising water in an amount of at least 60 percent by weight of the solvent, and the second coating composition having a viscosity of from 4 to 1,000 cP at 25 xc2x0 C., and the viscosity at 5 xc2x0 C. being at least 1.5 times higher than that at 25 xc2x0 C.
In the heat developable photosensitive material, the first coating composition and the second coating composition are preferably coated simultaneously, whereby the first layer and the second layer are formed.
In the heat developable photosensitive material, the second layer is preferably an outermost layer.
In the heat developable photosensitive material, the polymer latex in the second coating composition preferably has a glass transition point of from 25 to 70xc2x0 C.
In the heat developable photosensitive material, the polymer latex in the first coating composition preferably has a glass transition point of from xe2x88x9230 to 40xc2x00C.
In the heat developable photosensitive material, the first or second coating composition preferably comprises a phthalazine derivative.
In the heat developable photosensitive material, the second coating composition preferably comprises a thickening agent.
In the heat developable photosensitive material, the second coating composition is preferably gelled at a temperature which is at least 15xc2x0 C. lower than the temperature of the second coating composition at a time of coating.
In the heat developable photosensitive material, wherein the second coating composition preferably comprises a gelation promoting agent.
A method for preparation of a heat developable photosensitive material comprising
coating, on a support, a first coating composition containing the organic silver salt, the photosensitive silver halide, the reducing agent, polymer latex in an amount of at least 30 percent by weight of the first layer at dried state and a solvent, the solvent comprising water in an amount of at least 50 percent by weight of the solvent, to form a first layer and
coating, a second coating composition comprising a polymer latex in an amount of at least 50 percent of the second layer at dried state and a solvent, the solvent comprising water in an amount of at least 60 percent by weight of the solvent, and the second coating composition having a viscosity of from 4 to 1,000 cP at 25xc2x00C., and the viscosity at 5 xc2x0 C. being at least 1.5 times higher than that at 25xc2x0 C., to form a second layer in same side of the first layer provided farther from the support than the first layer.
In the method, the first coating composition and the second coating composition are preferably coated simultaneously.
In the method, the first coating composition or the second coating composition is preferably coated at a coating speed of from 50 to 400 m/minute.
In the method the method, drying is preferably carried out so that said material is not brought into contact with a conveying roller.
Other embodiments of the invention are further described.
1. A heat developable photosensitive material which is prepared by simultaneously coating a support with Coating Composition 1 which comprises a polymer latex in an amount of at least 30 percent by weight of a photographic constitution layer which is formed by said Coating Composition 1 comprising at least an organic silver salt, photosensitive silver halide, and a reducing agent, and which also comprises water in an amount of at least 50 percent by weight of the solvent, and Coating Composition 2 which comprises a polymer latex in an amount of at least 50 percent of a photographic constitution layer formed by employing said Coating Composition 2, comprises water in an amount of at least 60 percent by weight of the solvent, has a viscosity of from 50 to 1,000 cP at 25xc2x0 C., and also has a viscosity at 5xc2x0 C. which is at least 1.5 times higher than that at 25xc2x0 C. so that said Coating Composition 2 is coated on said Coating Composition 1 on said support.
2. The heat developable photosensitive material described in 1. above wherein the photographic constitution layer prepared by employing said Coating Composition 2 is the uppermost layer with respect to said support.
3. The heat developable photosensitive material described in 1. above wherein the polymer layer of said Coating Composition 2 has a glass transition point of from 25 to 70xc2x0 C.
4. The heat developable photosensitive material described in 1., 2. or 3. above wherein a phthalazine derivative is incorporated into either said Coating Composition 1 or said Coating Composition 2.
5. The heat developable photosensitive material described in any one of 1. through 4. above wherein said material is prepared employing a coating speed of from 50 to 400 m/minute.
6. The heat developable photosensitive martial described in 5. above wherein said material is prepared employing the drying process after said coating in which drying is carried out so that said material is not brought into contact with the conveying rollers.
7. A heat developable photosensitive material which is prepared by simultaneously coating onto a support Coating Composition 1, which comprises a polymer latex in an amount of at least 30 percent by weight of a photographic constitution layer which is formed by employing said Coating Composition 1, comprising at least an organic silver salt, photosensitive silver halide, and a reducing agent, and which also comprises water in an amount of at least 50 percent by weight of the solvent, and Coating Composition 2, which comprises a polymer latex in an amount of at least 50 percent of a photographic constitution layer formed by employing said Coating Composition 2, also comprises a thickener, comprises water in an amount of at least 60 percent by weight of the solvent, and has a viscosity of from 50 to 1,000 cP at 25xc2x0 C. so that said Coating Composition 2 is coated on said Coating Composition 1 on said support.
8. The heat developable photosensitive material described in 7. above wherein said thickener is subjected to gelation at a temperature of 15xc2x0 C. lower than the temperature during the coating of said Coating Composition 2.
9. The heat developable photosensitive material described in 7. or 8. above wherein said Coating Composition 2 comprises a gelation enhancing agent.
10. A heat developable photosensitive material which is prepared by simultaneously coating onto a support with Coating Composition 1 which comprises a polymer latex in an amount of at least 30 percent by weight of a photographic constitution layer which is formed by employing said Coating Composition 1, and comprises water in an amount of at least 60 percent by weight of solvents, and Coating Composition 2 which comprises a polymer latex in an amount of at least 50 percent of a photographic constitution layer which is formed by employing said Coating Composition 2, also comprises water in an amount of at least 60 percent by weight of solvents, and is gelled at a temperature which is at least 15xc2x0 C. lower than the temperature during coating so that said Coating Composition 2 is coated on said Coating Composition 1 on said support.
11. The heat developable photosensitive material described in 10. above wherein said Coating Composition 2 comprises a gelation promoting agent.